Conventional refrigeration systems are known which include a plurality of utilization side heat exchangers in a plurality of circuit lines, respectively, (see, for example, Patent Document 1). The refrigeration system includes a refrigerant circuit in which a compression mechanism, a heat-source side heat exchanger and utilization side heat exchangers included in two circuit lines are connected to operate in a refrigeration cycle. The two circuit lines including the utilization side heat exchangers are composed of: a first system including a chilling heat exchanger and a freezing heat exchanger both for cooling storage cases; and a second system including an indoor heat exchanger for cooling and heating a room. The compression mechanism is composed of a first compressor exclusive to the first system, a third compressor exclusive to the second system and a second compressor for backing up the first or second system.
The compression mechanism is connected at the suction side to a four-way selector valve. Specifically, this four-way selector valve has a first port connected to a branch pipe branched from a suction pipe for the first compressor, a second port connected to a suction pipe for the second compressor, a third port connected to a branch pipe branched from a suction pipe for the third compressor, and a fourth port connected to the discharge side of the compressor mechanism. The four-way selector valve is configured to be switchable between a first position in which the first and second ports are communicated with each other and the third and fourth ports are communicated with each other and a second position in which the first and fourth ports are communicated with each other and the second and third ports are communicated with each other. Thus, if the first system lacks the cooling capacity, the four-way selector valve switches to the first position whereby the second compressor is used for the first system to back up the first compressor. On the other hand, if the second system lacks the cooling/heating capacity, the four-way selector valve switches to the second position whereby the second compressor is used for the second system to back up the third compressor.    Patent Document 1: Published Japanese Patent Application No. 2004-44921